The optical atomic clocks have the potential to transform global timekeeping, relying on the state-of-the-art accuracy and stability, and greatly improve the measurement precision for a wide range of scientific and technological applications. Herein we report on the development of the optical clock based on 171Yb atoms confined in an optical lattice. A minimum width of 1.92-Hz Rabi spectra has been obtained with a new 578-nm clock interrogation laser. The in-loop fractional instability of the 171Yb clock reaches 9.1 × 10−18 after an averaging over a time of 2.0 × 104 s. By synchronous comparison between two clocks, we demonstrate that our 171Yb optical lattice clock achieves a fractional instability of 4.60 × 10 − 16 / τ .

We report on the absolute frequency measurement of the 6s 2 1 S 0 -6s6p 3 P 0 transition in 171 Yb with a fractional uncertainty of 7.3 × 10 -16 . A global positioning system carrier phase frequency transfer was established between National Institute of Metrology of China and East China Normal University, which linked the optical frequency of the ECNU Yb1 clock to the second in the International System of Units (SI) through international atomic time. Frequency measurements were carried out in 15 separate days with a total time over 3.8 × 10 5 s. The absolute frequency was determined to be 518 295 836 590 863.30(38) Hz. Our result is in good agreement with the recommended value in neutral Yb as a secondary representation of the SI second endorsed by the International Committee for Weights and Measures.

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